Heat sink



FIG. 1 is a perspective view of a heat sink in accordance with our design;

FIG. 2 is a top view thereof;

FIG. 3 is a sectional view taken along line 3—3 shown in FIG. 2; and,

FIG. 4 is a bottom view thereof.

Any shading on the figures is provided only to distinguish between the flat and contoured portions of the device, such shading patterns are not intended to be viewed as part of the claimed heat sink design.

The broken line showing portions of the heat sink is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a heat sink, as shown and described. 